1. Field of the Invention
The subject invention relates to a unique apparatus for continuous uniform heating synthetic fibers by resonant absorption of laser energy.
2. Description of the Prior Art
Thermoplastic man-made fibers can be permanently heat-set after drawing and orientation. The fiber will possess structural integrity and will maintain its desired configuration below the prescribed heat set temperature. Thermoplastic fibers or yarns from these fibers can be processed with conventional "long" and "short" direct contact heaters used for a variety of purposes in the textile industry. Yarns made from thermoplastic fiber in the form of a continuous filament are capable of a pronounced degree of stretch and rapid recovery and can be subjected to an appropriate combination of deforming, heat setting and development treatments. These yarns can also be bulked.
Twist yarn is made by a continuous process on the false twist principle, where two or more yarns are fed to a twister which inserts extra twist to double them, heat sets the yarns and then untwists the plural yarns and winds them on plural separate spools.
Conventional microfiber production typically consists of taking a higher denier fiber, placing it in a conventional contact heater and then directing the fiber to a drawing machine where it is stretched to a smaller diameter (smaller denier).
Conventional false twist and heat stretching may be accomplished by use of so-called "short heaters" or "long heaters".
The main advantages associated with conventional "short heaters" over "long heaters" include: (1) Relatively shorter yarn paths with the ability to have a truly linear yarn path; (2) Greater flexibility of process parameters and end products; (3) Self-cleaning properties of the heater; and (4) Better textile characteristics at today's existing speeds or higher production speeds and resultant identical textile characteristics.
With conventional "short heater" technology, heater temperatures generally are maintained in a substantially constant range regardless of the type of yarn or denier. For example, heavier denier polyester is typically heat treated within a temperature range of between about 205 degrees C. to about 215 degrees C. Higher temperature levels will generally vary with the type of raw material, the total denier, the denier per filament and the linear speed, thereby having a direct positive effect on reduction of power consumption. In addition, the consumed power of the high temperature short heater without yarn is dramatically reduced compared to today's conventional long heater technology on the basis of the much shorter length of 600 mm verses the 2,500 mm of the long heater. Typically, the heater surface in contact with the atmosphere is reduced four to five times, thereby minimizing loss of heat with a resultant decrease in consumed energy.
Conventional processing heaters, however, typically utilized direct-contact heat, for instance, a heated metal plate to heat the fiber. Such heaters are relatively inefficient because they heat not only the fiber being processed, but also the surrounding area. Additionally, conventional heaters are generally two to three meters in length, requiring relatively large processing area to accommodate such equipment.
Laser treatment of fibers is also known to the art. For instance, Japanese Patent No. 59-157,310 relates to a thick and thin synthetic fiber and a method for its manufacture. A method for manufacturing the thick fiber is disclosed having variations in refractive index in the direction of the fiber access and thick and thin sections which is characterized by the fact that the oriented thermoplastic synthetic fiber is subject to intermittent irradiation with laser light under tension. Accordingly, the Japanese patent disclosure is directed to varying the diameter of the fiber over its length by means of an intermittent heating or pulse heating to portions of the fiber.
Bossman, et al. in U.S. Pat. No. 5,017,423 discloses the use of a laser to remove material from the fiber that is to be treated to reduce the denier.
Macken, et al. in U.S. Pat. No. 4,156,124 discloses image transfer laser engraving. The Macken, et al. apparatus and method relies upon indexing of the work piece in relation to the pattern mask.
Kajikawa, in U.S. Pat. No. 4,950,862 discloses laser machining apparatus using a focusing lens array to delivery laser energy to the sample being treated.
Accordingly, there exists a need for an improved method and apparatus which will produce an even heating of the fiber in a uniform manner. Those skilled in the art have recognized a significant need for an improved process and apparatus for even and continuous heating to produce false twist and/or diameter reduction of the fiber such as by stretching, so that it results in a microfiber. Moreover, those skilled in the art recognized a significant need for processing equipment which will reduce the size of conventional "long heaters" and "short heaters" and which will be energy efficient. The present invention fulfills these needs.